<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<style>
#div1{
	width:100px;
	height:300px;
	position:absolute;
	bottom:0;
	left:0;
	background-color:red;
}
</style>
<script>
window.onscroll=function(){
	
	var oDiv=document.getElementById('div1');
	var scrollTop=document.documentElement.scrollTop || document.body.scrollTop;
	//oDiv.style.top=document.documentElement.clientHeight-oDiv.offsetHeight+scrollTop+'px';
	//startMove(document.documentElement.clientHeight-oDiv.offsetHeight+scrollTop);
	startMove(parseInt((document.documentElement.clientHeight-oDiv.offsetHeight)/2+scrollTop));
};
var timer=null;
function startMove(iTarget){//参数:目标点
	var oDiv=document.getElementById('div1');
	
	clearInterval(timer)//当我没有加的时候，滑动滚动条div不会动，反而上下抖动
	timer=setInterval(function(){
		var speed=(iTarget-oDiv.offsetTop)/6;
		
		speed=speed>0?Math.ceil(speed):Math.floor(speed);
		
		if(oDiv.offsetTop==iTarget)
		{
			clearInterval(timer);
		}
		else
		{
			document.title=iTarget+','+oDiv.offsetTop+','+oDiv.style.top;
			oDiv.style.top=oDiv.offsetTop+speed+'px';
		}
		;
		/**/
	},30)
};
</script>
</head>

<body style="height:2000px;">
<input type="txt1" style="position:fixed;top:0;left:0;"/>
<div id="div1">
</div>

</body>
</html>
